Persons skilled in the art know that the cultivation of citrus fruits is the main national fruit sector. Half the citrus fruits produced in Spain are intended for export, therefore Spanish citrus fruits occupy a very important place in the context of producer countries. However, the low production costs of non-European countries of the Mediterranean area allow their citriculture to compete advantageously on the market against Spanish productions. If this is added to the progressive opening of the European Union markets to these countries, the only alternatives that seem to be possible for maintaining the market share consist of offering a product with a better quality than the competing countries, together with a reduction in the production costs.
The quality of the fruit is determined by aspects such as the presentation, the appearance, the uniformity, the ripeness and the freshness, all of them being essential components of the purchase decision. The quality of the fruits can be affected by various reasons, giving rise to morphological and physiological defects devaluating the product. The most worrying causes include those generating defects in the fruit during or after the preparation for the market, and which show in the places of sale. The mechanical damage or lesions taking place while handling the product are the entryway for multiple pathogens causing rot, such as fungi of the Botrytis, Rhizopus, Alternaria, Geotrichum genera, but especially the Penicillium digitatum (green mold) and Penicillium italicum (blue mold) fungi, causing most of the post-harvest infections.
Losses due to rot are of the order of 3-5% of all the fruits handled in centers, reaching the order of 7-12% in abnormal weather years. To reduce these losses, several sorting operations are carried out in the fruit processing plant, considering criteria such as defects in the skin, presence of insects, damage due to hail, deformed fruits, etc. However, this operation is not always effective due to the possibility that, at the time of the sorting, the damage caused by rot is still not externally visible. In these conditions, the fungus will develop during storage and transport, spreading the infection throughout the entire batch and causing large economic losses. A quick detection of the infection will be especially important to maintain the quality of the product and prevent economic losses to thus be able to compete in better conditions on the market.
The use of ultraviolet light to detect the infection in the fruit before it develops externally is currently known in the state of the art. The known method is essentially based on the fact that, when the infection caused by the fungus progresses, the chemical composition of the fruit tissues is altered, the essential oils contained in the glands of the skin being spilled; the illumination of these tissues with UV light shows their fluorescence, making damage which is still latent visible.
UV rays form the band of the electromagnetic spectrum comprised between 100-400 nm, adjoining X-rays and the visible band. The light is generally divided into three bands with the following wavelengths: UV-C, 100-280 nm; UV-B, 280-315 nm; UV-A, 315-400 nm.
The sorting operation making use of UV light is carried out manually in special inspection chambers located in the processing line and usually known as “discotheques”. These chambers consist of dark cabinets, with small dimensions, illuminated only with black light tubes; these tubes emit a wavelength corresponding with the UV-A band. The fruit developing fluorescence upon passing through the cabinet indicates that the infection is latent and will be immediately eliminated from the line. The fruits pass over rollers rotating and making the fruits rotate such that substantially the entire surface of the fruit can be seen.
However, the use of UV light in this mode of inspection has several drawbacks. In fact, UV radiations are, among non-ionizing radiations, those with the greatest energy content. This relatively high energy content makes them capable of chemically reacting with matter, causing the so-called photochemical reactions. The biological effects of UV rays mainly affect the skin, causing erythemas, loss of elasticity and delayed melanogenesis. This type of radiation can also cause ophthalmic diseases such as keratitis, conjunctivitis and cataracts. For these reasons, UV lamps are considered a Group I risk by the Illuminating Engineering Society (ANSI/IESNA RP-27.3-96).
Practical recommendations have been established for the safe photo-biological use of UV light lamps. These recommendations are based on tolerable radiation limits. Thus, for lamps emitting radiation with wavelengths comprised between 320 and 400 nm, the energy flow must not exceed 1 mW/cm2 and the exposure time must be limited, to a greater extent the lower the distance to the emitting source. According to these recommendations, the operators working in these inspection cabinets work in shifts in order to not remain in the cabinets for a time greater than one hour. Another recommendation consists of using protective gloves and goggles absorbing the UV radiation received, reducing the exposure of the operator to non-hazardous levels (RD-773/1997 and RD-1002/2002). Specific and periodic medical examinations and radiation measurements will be carried out to control these aspects.
The manual selection work in these conditions is tedious and repetitive for the operators. Additionally, this labor represents a considerable cost for the company.
Analysis techniques have therefore progressed during the last few years for the purpose of achieving fruit classification and rejection systems which allow reducing the high personnel costs directly related to this process. In this sense, the automation of these tasks will allow improving the quality of the work of these operators, since it is carried out automatically, the job of the operator being limited to supervising the correct operation of the system from the outside through control monitors.
There is currently no knowledge of the existence on the market of an automatic system which allows detecting rot of fruits making use of the fluorescence of the essential oils upon applying UV light, despite the intense research being conducted in relation to this type of system.
The present invention belongs to the sector of the systems responsible for the detection of pieces of fruit, especially citrus fruits, having any amount of rot, and has been developed for the purpose of providing effective solutions to the problems existing in the installations of the current state of the art. This objective has been fully reached by means of the system the embodiments of which will be the object of the description below, and the main features of which are included in the characterizing portion of the attached claim 1. The dependent claims define the details and particulars of the system of the invention.
The system of the invention is essentially intended for the physical separation of the fruits having any type of rot passing through a treatment and calibration line, by means of the automatic expulsion of the affected fruits, and it therefore automatically carries out the same job which was being performed manually up until now.
The operation principle of the system is based on using black light, more specifically light belonging to the UV-A band, to detect the rot which may be developing in citrus fruits, in the same way as it is used in manual sorting. To that end, the system uses the observed feature that the essential oils coming out during the development of the rot react when UV light impinges on them, emitting fluorescence. This fluorescence is a radiation with rather low intensity, and with a very important component of wavelengths centered in the green-yellow band. This fluorescence is that identified in the images captured by a camera to determine if the fruit is affected by any type of rot.
To achieve this objective, a system has been designed which in its preferred embodiment comprises a first unit acting as a computer vision member, in which the fruit passing on a conveyor means is illuminated with ultraviolet light, such that in the event that any rot is detected on one or more specific pieces, the fluorescence emitted by the latter will be captured by the computer vision system. This situation is detected by the identification and control member, preferably a computer, from where a command is sent to an expulsion assembly incorporated in a corresponding unit located after the computer vision unit, such that the piece (or pieces) of citrus fruit identified as rotten are expelled from the conveyor means when they reach the corresponding position. The exact position of the piece of fruit which must be expelled is determined with the aid of a conventional encoder.
In this simple but highly efficient manner, the system identifies the rotten piece of fruit and automatically expels it from the conveyor means without needing human intervention.
Additionally, in an alternative embodiment of the invention which has been developed to perform a more precise identification of the damaged fruits, the invention has provided several modifications intended to improve the functionality of the described system by means of providing other alternative capacities complementary to those implemented by the first embodiment and aimed at a more perfect view of the fruits when they pass through the installation with better selection assurances.
Essentially, these improvements proposed by the second embodiment of the present invention basically consist of a change in the number and in the position of the computer vision members, such that instead of a single vision member two different members are used, located in aligned opposite positions according to a line transverse to the passage of the fruits, separated by a certain distance, such that the suitably illuminated fruits are viewed from different positions, thus assuring that a much broader surface of each fruit is viewed in each case, thus eliminating possible classification errors derived from possible “dead spots” which cannot be observed with the use of a single computer vision member, despite the fact that the fruits can be rotated upon advancing through the installation.
Furthermore, to implement said second embodiment, a thorough selection of the computer vision members has been carried out, based on MAF type cameras equipped with 2 monochromatic sensors, one of which is intended for the detection of fluorescences and the other of which, equipped with suitable NIR filters, allows observing slight variations in the images caused by the impingement on the damaged area of the small near IR component inherent to UV light emitted to illuminate the fruits when they pass through the detection area.